/**
 * @file
 * Dynamic memory manager
 *
 * This is a lightweight replacement for the standard C library malloc().
 *
 * If you want to use the standard C library malloc() instead, define
 * MEM_LIBC_MALLOC to 1 in your lwipopts.h
 *
 * To let mem_malloc() use pools (prevents fragmentation and is much faster than
 * a heap but might waste some memory), define MEM_USE_POOLS to 1, define
 * MEMP_USE_CUSTOM_POOLS to 1 and create a file "lwippools.h" that includes a list
 * of pools like this (more pools can be added between _START and _END):
 *
 * Define three pools with sizes 256, 512, and 1512 bytes
 * LWIP_MALLOC_MEMPOOL_START
 * LWIP_MALLOC_MEMPOOL(20, 256)
 * LWIP_MALLOC_MEMPOOL(10, 512)
 * LWIP_MALLOC_MEMPOOL(5, 1512)
 * LWIP_MALLOC_MEMPOOL_END
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *         Simon Goldschmidt
 *
 */

#include "lwip/opt.h"
#include "lwip/mem.h"
#include "lwip/def.h"
#include "lwip/sys.h"
#include "lwip/stats.h"
#include "lwip/err.h"

#include <string.h>

#if MEM_LIBC_MALLOC
#include <stdlib.h> /* for malloc()/free() */
#endif

#if MEM_LIBC_MALLOC || MEM_USE_POOLS

/** mem_init is not used when using pools instead of a heap or using
 * C library malloc().
 */
void
mem_init(void)
{
}

/** mem_trim is not used when using pools instead of a heap or using
 * C library malloc(): we can't free part of a pool element and the stack
 * support mem_trim() to return a different pointer
 */
void *
mem_trim(void *mem, mem_size_t size)
{
    LWIP_UNUSED_ARG(size);
    return mem;
}
#endif /* MEM_LIBC_MALLOC || MEM_USE_POOLS */

#if MEM_LIBC_MALLOC
/* lwIP heap implemented using C library malloc() */

/* in case C library malloc() needs extra protection,
 * allow these defines to be overridden.
 */
#ifndef mem_clib_free
#define mem_clib_free free
#endif
#ifndef mem_clib_malloc
#define mem_clib_malloc malloc
#endif
#ifndef mem_clib_calloc
#define mem_clib_calloc calloc
#endif

#if LWIP_STATS && MEM_STATS
#define MEM_LIBC_STATSHELPER_SIZE LWIP_MEM_ALIGN_SIZE(sizeof(mem_size_t))
#else
#define MEM_LIBC_STATSHELPER_SIZE 0
#endif

/**
 * Allocate a block of memory with a minimum of 'size' bytes.
 *
 * @param size is the minimum size of the requested block in bytes.
 * @return pointer to allocated memory or NULL if no free memory was found.
 *
 * Note that the returned value must always be aligned (as defined by MEM_ALIGNMENT).
 */
void *
mem_malloc(mem_size_t size)
{
    void *ret = mem_clib_malloc(size + MEM_LIBC_STATSHELPER_SIZE);
    if (ret == NULL)
    {
        MEM_STATS_INC(err);
    }
    else
    {
        LWIP_ASSERT("malloc() must return aligned memory", LWIP_MEM_ALIGN(ret) == ret);
#if LWIP_STATS && MEM_STATS
        *(mem_size_t *)ret = size;
        ret = (u8_t *)ret + MEM_LIBC_STATSHELPER_SIZE;
        MEM_STATS_INC_USED(used, size);
#endif
    }
    return ret;
}

/** Put memory back on the heap
 *
 * @param rmem is the pointer as returned by a previous call to mem_malloc()
 */
void
mem_free(void *rmem)
{
    LWIP_ASSERT("rmem != NULL", (rmem != NULL));
    LWIP_ASSERT("rmem == MEM_ALIGN(rmem)", (rmem == LWIP_MEM_ALIGN(rmem)));
#if LWIP_STATS && MEM_STATS
    rmem = (u8_t *)rmem - MEM_LIBC_STATSHELPER_SIZE;
    MEM_STATS_DEC_USED(used, *(mem_size_t *)rmem);
#endif
    mem_clib_free(rmem);
}

#elif MEM_USE_POOLS

/* lwIP heap implemented with different sized pools */

/**
 * Allocate memory: determine the smallest pool that is big enough
 * to contain an element of 'size' and get an element from that pool.
 *
 * @param size the size in bytes of the memory needed
 * @return a pointer to the allocated memory or NULL if the pool is empty
 */
void *
mem_malloc(mem_size_t size)
{
    void *ret;
    struct memp_malloc_helper *element = NULL;
    memp_t poolnr;
    mem_size_t required_size = size + LWIP_MEM_ALIGN_SIZE(sizeof(struct memp_malloc_helper));

    for (poolnr = MEMP_POOL_FIRST; poolnr <= MEMP_POOL_LAST; poolnr = (memp_t)(poolnr + 1))
    {
        /* is this pool big enough to hold an element of the required size
           plus a struct memp_malloc_helper that saves the pool this element came from? */
        if (required_size <= memp_pools[poolnr]->size)
        {
            element = (struct memp_malloc_helper *)memp_malloc(poolnr);
            if (element == NULL)
            {
                /* No need to DEBUGF or ASSERT: This error is already taken care of in memp.c */
#if MEM_USE_POOLS_TRY_BIGGER_POOL
                /** Try a bigger pool if this one is empty! */
                if (poolnr < MEMP_POOL_LAST)
                {
                    continue;
                }
#endif /* MEM_USE_POOLS_TRY_BIGGER_POOL */
                MEM_STATS_INC(err);
                return NULL;
            }
            break;
        }
    }
    if (poolnr > MEMP_POOL_LAST)
    {
        LWIP_ASSERT("mem_malloc(): no pool is that big!", 0);
        MEM_STATS_INC(err);
        return NULL;
    }

    /* save the pool number this element came from */
    element->poolnr = poolnr;
    /* and return a pointer to the memory directly after the struct memp_malloc_helper */
    ret = (u8_t *)element + LWIP_MEM_ALIGN_SIZE(sizeof(struct memp_malloc_helper));

#if MEMP_OVERFLOW_CHECK || (LWIP_STATS && MEM_STATS)
    /* truncating to u16_t is safe because struct memp_desc::size is u16_t */
    element->size = (u16_t)size;
    MEM_STATS_INC_USED(used, element->size);
#endif /* MEMP_OVERFLOW_CHECK || (LWIP_STATS && MEM_STATS) */
#if MEMP_OVERFLOW_CHECK
    /* initialize unused memory (diff between requested size and selected pool's size) */
    memset((u8_t *)ret + size, 0xcd, memp_pools[poolnr]->size - size);
#endif /* MEMP_OVERFLOW_CHECK */
    return ret;
}

/**
 * Free memory previously allocated by mem_malloc. Loads the pool number
 * and calls memp_free with that pool number to put the element back into
 * its pool
 *
 * @param rmem the memory element to free
 */
void
mem_free(void *rmem)
{
    struct memp_malloc_helper *hmem;

    LWIP_ASSERT("rmem != NULL", (rmem != NULL));
    LWIP_ASSERT("rmem == MEM_ALIGN(rmem)", (rmem == LWIP_MEM_ALIGN(rmem)));

    /* get the original struct memp_malloc_helper */
    /* cast through void* to get rid of alignment warnings */
    hmem = (struct memp_malloc_helper *)(void *)((u8_t *)rmem - LWIP_MEM_ALIGN_SIZE(sizeof(struct memp_malloc_helper)));

    LWIP_ASSERT("hmem != NULL", (hmem != NULL));
    LWIP_ASSERT("hmem == MEM_ALIGN(hmem)", (hmem == LWIP_MEM_ALIGN(hmem)));
    LWIP_ASSERT("hmem->poolnr < MEMP_MAX", (hmem->poolnr < MEMP_MAX));

    MEM_STATS_DEC_USED(used, hmem->size);
#if MEMP_OVERFLOW_CHECK
    {
        u16_t i;
        LWIP_ASSERT("MEM_USE_POOLS: invalid chunk size",
                    hmem->size <= memp_pools[hmem->poolnr]->size);
        /* check that unused memory remained untouched (diff between requested size and selected pool's size) */
        for (i = hmem->size; i < memp_pools[hmem->poolnr]->size; i++)
        {
            u8_t data = *((u8_t *)rmem + i);
            LWIP_ASSERT("MEM_USE_POOLS: mem overflow detected", data == 0xcd);
        }
    }
#endif /* MEMP_OVERFLOW_CHECK */

    /* and put it in the pool we saved earlier */
    memp_free(hmem->poolnr, hmem);
}

#else /* MEM_USE_POOLS */
/* lwIP replacement for your libc malloc() */

/**
 * The heap is made up as a list of structs of this type.
 * This does not have to be aligned since for getting its size,
 * we only use the macro SIZEOF_STRUCT_MEM, which automatically aligns.
 */
struct mem
{
    /** index (-> ram[next]) of the next struct */
    mem_size_t next;
    /** index (-> ram[prev]) of the previous struct */
    mem_size_t prev;
    /** 1: this area is used; 0: this area is unused */
    u8_t used;
};

/** All allocated blocks will be MIN_SIZE bytes big, at least!
 * MIN_SIZE can be overridden to suit your needs. Smaller values save space,
 * larger values could prevent too small blocks to fragment the RAM too much. */
#ifndef MIN_SIZE
#define MIN_SIZE             12
#endif /* MIN_SIZE */
/* some alignment macros: we define them here for better source code layout */
#define MIN_SIZE_ALIGNED     LWIP_MEM_ALIGN_SIZE(MIN_SIZE)
#define SIZEOF_STRUCT_MEM    LWIP_MEM_ALIGN_SIZE(sizeof(struct mem))
#define MEM_SIZE_ALIGNED     LWIP_MEM_ALIGN_SIZE(MEM_SIZE)

/** If you want to relocate the heap to external memory, simply define
 * LWIP_RAM_HEAP_POINTER as a void-pointer to that location.
 * If so, make sure the memory at that location is big enough (see below on
 * how that space is calculated). */
#ifndef LWIP_RAM_HEAP_POINTER
/** the heap. we need one struct mem at the end and some room for alignment */
LWIP_DECLARE_MEMORY_ALIGNED(ram_heap, MEM_SIZE_ALIGNED + (2U * SIZEOF_STRUCT_MEM));
#define LWIP_RAM_HEAP_POINTER ram_heap
#endif /* LWIP_RAM_HEAP_POINTER */

/** pointer to the heap (ram_heap): for alignment, ram is now a pointer instead of an array */
static u8_t *ram;
/** the last entry, always unused! */
static struct mem *ram_end;
/** pointer to the lowest free block, this is used for faster search */
static struct mem *lfree;

/** concurrent access protection */
#if !NO_SYS
static sys_mutex_t mem_mutex;
#endif

#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT

static volatile u8_t mem_free_count;

/* Allow mem_free from other (e.g. interrupt) context */
#define LWIP_MEM_FREE_DECL_PROTECT()  SYS_ARCH_DECL_PROTECT(lev_free)
#define LWIP_MEM_FREE_PROTECT()       SYS_ARCH_PROTECT(lev_free)
#define LWIP_MEM_FREE_UNPROTECT()     SYS_ARCH_UNPROTECT(lev_free)
#define LWIP_MEM_ALLOC_DECL_PROTECT() SYS_ARCH_DECL_PROTECT(lev_alloc)
#define LWIP_MEM_ALLOC_PROTECT()      SYS_ARCH_PROTECT(lev_alloc)
#define LWIP_MEM_ALLOC_UNPROTECT()    SYS_ARCH_UNPROTECT(lev_alloc)

#else /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */

/* Protect the heap only by using a semaphore */
#define LWIP_MEM_FREE_DECL_PROTECT()
#define LWIP_MEM_FREE_PROTECT()    sys_mutex_lock(&mem_mutex)
#define LWIP_MEM_FREE_UNPROTECT()  sys_mutex_unlock(&mem_mutex)
/* mem_malloc is protected using semaphore AND LWIP_MEM_ALLOC_PROTECT */
#define LWIP_MEM_ALLOC_DECL_PROTECT()
#define LWIP_MEM_ALLOC_PROTECT()
#define LWIP_MEM_ALLOC_UNPROTECT()

#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */


/**
 * "Plug holes" by combining adjacent empty struct mems.
 * After this function is through, there should not exist
 * one empty struct mem pointing to another empty struct mem.
 *
 * @param mem this points to a struct mem which just has been freed
 * @internal this function is only called by mem_free() and mem_trim()
 *
 * This assumes access to the heap is protected by the calling function
 * already.
 */
static void
plug_holes(struct mem *mem)
{
    struct mem *nmem;
    struct mem *pmem;

    LWIP_ASSERT("plug_holes: mem >= ram", (u8_t *)mem >= ram);
    LWIP_ASSERT("plug_holes: mem < ram_end", (u8_t *)mem < (u8_t *)ram_end);
    LWIP_ASSERT("plug_holes: mem->used == 0", mem->used == 0);

    /* plug hole forward */
    LWIP_ASSERT("plug_holes: mem->next <= MEM_SIZE_ALIGNED", mem->next <= MEM_SIZE_ALIGNED);

    nmem = (struct mem *)(void *)&ram[mem->next];
    if (mem != nmem && nmem->used == 0 && (u8_t *)nmem != (u8_t *)ram_end)
    {
        /* if mem->next is unused and not end of ram, combine mem and mem->next */
        if (lfree == nmem)
        {
            lfree = mem;
        }
        mem->next = nmem->next;
        ((struct mem *)(void *)&ram[nmem->next])->prev = (mem_size_t)((u8_t *)mem - ram);
    }

    /* plug hole backward */
    pmem = (struct mem *)(void *)&ram[mem->prev];
    if (pmem != mem && pmem->used == 0)
    {
        /* if mem->prev is unused, combine mem and mem->prev */
        if (lfree == mem)
        {
            lfree = pmem;
        }
        pmem->next = mem->next;
        ((struct mem *)(void *)&ram[mem->next])->prev = (mem_size_t)((u8_t *)pmem - ram);
    }
}

/**
 * Zero the heap and initialize start, end and lowest-free
 */
void
mem_init(void)
{
    struct mem *mem;

    LWIP_ASSERT("Sanity check alignment",
                (SIZEOF_STRUCT_MEM & (MEM_ALIGNMENT - 1)) == 0);

    /* align the heap */
    ram = (u8_t *)LWIP_MEM_ALIGN(LWIP_RAM_HEAP_POINTER);
    /* initialize the start of the heap */
    mem = (struct mem *)(void *)ram;
    mem->next = MEM_SIZE_ALIGNED;
    mem->prev = 0;
    mem->used = 0;
    /* initialize the end of the heap */
    ram_end = (struct mem *)(void *)&ram[MEM_SIZE_ALIGNED];
    ram_end->used = 1;
    ram_end->next = MEM_SIZE_ALIGNED;
    ram_end->prev = MEM_SIZE_ALIGNED;

    /* initialize the lowest-free pointer to the start of the heap */
    lfree = (struct mem *)(void *)ram;

    MEM_STATS_AVAIL(avail, MEM_SIZE_ALIGNED);

    if (sys_mutex_new(&mem_mutex) != ERR_OK)
    {
        LWIP_ASSERT("failed to create mem_mutex", 0);
    }
}

/**
 * Put a struct mem back on the heap
 *
 * @param rmem is the data portion of a struct mem as returned by a previous
 *             call to mem_malloc()
 */
void
mem_free(void *rmem)
{
    struct mem *mem;
    LWIP_MEM_FREE_DECL_PROTECT();

    if (rmem == NULL)
    {
        LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("mem_free(p == NULL) was called.\n"));
        return;
    }
    LWIP_ASSERT("mem_free: sanity check alignment", (((mem_ptr_t)rmem) & (MEM_ALIGNMENT - 1)) == 0);

    LWIP_ASSERT("mem_free: legal memory", (u8_t *)rmem >= (u8_t *)ram &&
                (u8_t *)rmem < (u8_t *)ram_end);

    if ((u8_t *)rmem < (u8_t *)ram || (u8_t *)rmem >= (u8_t *)ram_end)
    {
        SYS_ARCH_DECL_PROTECT(lev);
        LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_free: illegal memory\n"));
        /* protect mem stats from concurrent access */
        SYS_ARCH_PROTECT(lev);
        MEM_STATS_INC(illegal);
        SYS_ARCH_UNPROTECT(lev);
        return;
    }
    /* protect the heap from concurrent access */
    LWIP_MEM_FREE_PROTECT();
    /* Get the corresponding struct mem ... */
    /* cast through void* to get rid of alignment warnings */
    mem = (struct mem *)(void *)((u8_t *)rmem - SIZEOF_STRUCT_MEM);
    /* ... which has to be in a used state ... */
    LWIP_ASSERT("mem_free: mem->used", mem->used);
    /* ... and is now unused. */
    mem->used = 0;

    if (mem < lfree)
    {
        /* the newly freed struct is now the lowest */
        lfree = mem;
    }

    MEM_STATS_DEC_USED(used, mem->next - (mem_size_t)(((u8_t *)mem - ram)));

    /* finally, see if prev or next are free also */
    plug_holes(mem);
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
    mem_free_count = 1;
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
    LWIP_MEM_FREE_UNPROTECT();
}

/**
 * Shrink memory returned by mem_malloc().
 *
 * @param rmem pointer to memory allocated by mem_malloc the is to be shrinked
 * @param newsize required size after shrinking (needs to be smaller than or
 *                equal to the previous size)
 * @return for compatibility reasons: is always == rmem, at the moment
 *         or NULL if newsize is > old size, in which case rmem is NOT touched
 *         or freed!
 */
void *
mem_trim(void *rmem, mem_size_t newsize)
{
    mem_size_t size;
    mem_size_t ptr, ptr2;
    struct mem *mem, *mem2;
    /* use the FREE_PROTECT here: it protects with sem OR SYS_ARCH_PROTECT */
    LWIP_MEM_FREE_DECL_PROTECT();

    /* Expand the size of the allocated memory region so that we can
       adjust for alignment. */
    newsize = LWIP_MEM_ALIGN_SIZE(newsize);

    if (newsize < MIN_SIZE_ALIGNED)
    {
        /* every data block must be at least MIN_SIZE_ALIGNED long */
        newsize = MIN_SIZE_ALIGNED;
    }

    if (newsize > MEM_SIZE_ALIGNED)
    {
        return NULL;
    }

    LWIP_ASSERT("mem_trim: legal memory", (u8_t *)rmem >= (u8_t *)ram &&
                (u8_t *)rmem < (u8_t *)ram_end);

    if ((u8_t *)rmem < (u8_t *)ram || (u8_t *)rmem >= (u8_t *)ram_end)
    {
        SYS_ARCH_DECL_PROTECT(lev);
        LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_trim: illegal memory\n"));
        /* protect mem stats from concurrent access */
        SYS_ARCH_PROTECT(lev);
        MEM_STATS_INC(illegal);
        SYS_ARCH_UNPROTECT(lev);
        return rmem;
    }
    /* Get the corresponding struct mem ... */
    /* cast through void* to get rid of alignment warnings */
    mem = (struct mem *)(void *)((u8_t *)rmem - SIZEOF_STRUCT_MEM);
    /* ... and its offset pointer */
    ptr = (mem_size_t)((u8_t *)mem - ram);

    size = mem->next - ptr - SIZEOF_STRUCT_MEM;
    LWIP_ASSERT("mem_trim can only shrink memory", newsize <= size);
    if (newsize > size)
    {
        /* not supported */
        return NULL;
    }
    if (newsize == size)
    {
        /* No change in size, simply return */
        return rmem;
    }

    /* protect the heap from concurrent access */
    LWIP_MEM_FREE_PROTECT();

    mem2 = (struct mem *)(void *)&ram[mem->next];
    if (mem2->used == 0)
    {
        /* The next struct is unused, we can simply move it at little */
        mem_size_t next;
        /* remember the old next pointer */
        next = mem2->next;
        /* create new struct mem which is moved directly after the shrinked mem */
        ptr2 = ptr + SIZEOF_STRUCT_MEM + newsize;
        if (lfree == mem2)
        {
            lfree = (struct mem *)(void *)&ram[ptr2];
        }
        mem2 = (struct mem *)(void *)&ram[ptr2];
        mem2->used = 0;
        /* restore the next pointer */
        mem2->next = next;
        /* link it back to mem */
        mem2->prev = ptr;
        /* link mem to it */
        mem->next = ptr2;
        /* last thing to restore linked list: as we have moved mem2,
         * let 'mem2->next->prev' point to mem2 again. but only if mem2->next is not
         * the end of the heap */
        if (mem2->next != MEM_SIZE_ALIGNED)
        {
            ((struct mem *)(void *)&ram[mem2->next])->prev = ptr2;
        }
        MEM_STATS_DEC_USED(used, (size - newsize));
        /* no need to plug holes, we've already done that */
    }
    else if (newsize + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED <= size)
    {
        /* Next struct is used but there's room for another struct mem with
         * at least MIN_SIZE_ALIGNED of data.
         * Old size ('size') must be big enough to contain at least 'newsize' plus a struct mem
         * ('SIZEOF_STRUCT_MEM') with some data ('MIN_SIZE_ALIGNED').
         * @todo we could leave out MIN_SIZE_ALIGNED. We would create an empty
         *       region that couldn't hold data, but when mem->next gets freed,
         *       the 2 regions would be combined, resulting in more free memory */
        ptr2 = ptr + SIZEOF_STRUCT_MEM + newsize;
        mem2 = (struct mem *)(void *)&ram[ptr2];
        if (mem2 < lfree)
        {
            lfree = mem2;
        }
        mem2->used = 0;
        mem2->next = mem->next;
        mem2->prev = ptr;
        mem->next = ptr2;
        if (mem2->next != MEM_SIZE_ALIGNED)
        {
            ((struct mem *)(void *)&ram[mem2->next])->prev = ptr2;
        }
        MEM_STATS_DEC_USED(used, (size - newsize));
        /* the original mem->next is used, so no need to plug holes! */
    }
    /* else {
      next struct mem is used but size between mem and mem2 is not big enough
      to create another struct mem
      -> don't do anyhting.
      -> the remaining space stays unused since it is too small
    } */
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
    mem_free_count = 1;
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
    LWIP_MEM_FREE_UNPROTECT();
    return rmem;
}

/**
 * Allocate a block of memory with a minimum of 'size' bytes.
 *
 * @param size is the minimum size of the requested block in bytes.
 * @return pointer to allocated memory or NULL if no free memory was found.
 *
 * Note that the returned value will always be aligned (as defined by MEM_ALIGNMENT).
 */
void *
mem_malloc(mem_size_t size)
{
    mem_size_t ptr, ptr2;
    struct mem *mem, *mem2;
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
    u8_t local_mem_free_count = 0;
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
    LWIP_MEM_ALLOC_DECL_PROTECT();

    if (size == 0)
    {
        return NULL;
    }

    /* Expand the size of the allocated memory region so that we can
       adjust for alignment. */
    size = LWIP_MEM_ALIGN_SIZE(size);

    if (size < MIN_SIZE_ALIGNED)
    {
        /* every data block must be at least MIN_SIZE_ALIGNED long */
        size = MIN_SIZE_ALIGNED;
    }

    if (size > MEM_SIZE_ALIGNED)
    {
        return NULL;
    }

    /* protect the heap from concurrent access */
    sys_mutex_lock(&mem_mutex);
    LWIP_MEM_ALLOC_PROTECT();
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
    /* run as long as a mem_free disturbed mem_malloc or mem_trim */
    do
    {
        local_mem_free_count = 0;
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */

        /* Scan through the heap searching for a free block that is big enough,
         * beginning with the lowest free block.
         */
        for (ptr = (mem_size_t)((u8_t *)lfree - ram); ptr < MEM_SIZE_ALIGNED - size;
                ptr = ((struct mem *)(void *)&ram[ptr])->next)
        {
            mem = (struct mem *)(void *)&ram[ptr];
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
            mem_free_count = 0;
            LWIP_MEM_ALLOC_UNPROTECT();
            /* allow mem_free or mem_trim to run */
            LWIP_MEM_ALLOC_PROTECT();
            if (mem_free_count != 0)
            {
                /* If mem_free or mem_trim have run, we have to restart since they
                   could have altered our current struct mem. */
                local_mem_free_count = 1;
                break;
            }
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */

            if ((!mem->used) &&
                    (mem->next - (ptr + SIZEOF_STRUCT_MEM)) >= size)
            {
                /* mem is not used and at least perfect fit is possible:
                 * mem->next - (ptr + SIZEOF_STRUCT_MEM) gives us the 'user data size' of mem */

                if (mem->next - (ptr + SIZEOF_STRUCT_MEM) >= (size + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED))
                {
                    /* (in addition to the above, we test if another struct mem (SIZEOF_STRUCT_MEM) containing
                     * at least MIN_SIZE_ALIGNED of data also fits in the 'user data space' of 'mem')
                     * -> split large block, create empty remainder,
                     * remainder must be large enough to contain MIN_SIZE_ALIGNED data: if
                     * mem->next - (ptr + (2*SIZEOF_STRUCT_MEM)) == size,
                     * struct mem would fit in but no data between mem2 and mem2->next
                     * @todo we could leave out MIN_SIZE_ALIGNED. We would create an empty
                     *       region that couldn't hold data, but when mem->next gets freed,
                     *       the 2 regions would be combined, resulting in more free memory
                     */
                    ptr2 = ptr + SIZEOF_STRUCT_MEM + size;
                    /* create mem2 struct */
                    mem2 = (struct mem *)(void *)&ram[ptr2];
                    mem2->used = 0;
                    mem2->next = mem->next;
                    mem2->prev = ptr;
                    /* and insert it between mem and mem->next */
                    mem->next = ptr2;
                    mem->used = 1;

                    if (mem2->next != MEM_SIZE_ALIGNED)
                    {
                        ((struct mem *)(void *)&ram[mem2->next])->prev = ptr2;
                    }
                    MEM_STATS_INC_USED(used, (size + SIZEOF_STRUCT_MEM));
                }
                else
                {
                    /* (a mem2 struct does no fit into the user data space of mem and mem->next will always
                     * be used at this point: if not we have 2 unused structs in a row, plug_holes should have
                     * take care of this).
                     * -> near fit or exact fit: do not split, no mem2 creation
                     * also can't move mem->next directly behind mem, since mem->next
                     * will always be used at this point!
                     */
                    mem->used = 1;
                    MEM_STATS_INC_USED(used, mem->next - (mem_size_t)((u8_t *)mem - ram));
                }
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
mem_malloc_adjust_lfree:
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
                if (mem == lfree)
                {
                    struct mem *cur = lfree;
                    /* Find next free block after mem and update lowest free pointer */
                    while (cur->used && cur != ram_end)
                    {
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
                        mem_free_count = 0;
                        LWIP_MEM_ALLOC_UNPROTECT();
                        /* prevent high interrupt latency... */
                        LWIP_MEM_ALLOC_PROTECT();
                        if (mem_free_count != 0)
                        {
                            /* If mem_free or mem_trim have run, we have to restart since they
                               could have altered our current struct mem or lfree. */
                            goto mem_malloc_adjust_lfree;
                        }
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
                        cur = (struct mem *)(void *)&ram[cur->next];
                    }
                    lfree = cur;
                    LWIP_ASSERT("mem_malloc: !lfree->used", ((lfree == ram_end) || (!lfree->used)));
                }
                LWIP_MEM_ALLOC_UNPROTECT();
                sys_mutex_unlock(&mem_mutex);
                LWIP_ASSERT("mem_malloc: allocated memory not above ram_end.",
                            (mem_ptr_t)mem + SIZEOF_STRUCT_MEM + size <= (mem_ptr_t)ram_end);
                LWIP_ASSERT("mem_malloc: allocated memory properly aligned.",
                            ((mem_ptr_t)mem + SIZEOF_STRUCT_MEM) % MEM_ALIGNMENT == 0);
                LWIP_ASSERT("mem_malloc: sanity check alignment",
                            (((mem_ptr_t)mem) & (MEM_ALIGNMENT - 1)) == 0);

                return (u8_t *)mem + SIZEOF_STRUCT_MEM;
            }
        }
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
        /* if we got interrupted by a mem_free, try again */
    }
    while (local_mem_free_count != 0);
#endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("mem_malloc: could not allocate %"S16_F" bytes\n", (s16_t)size));
    MEM_STATS_INC(err);
    LWIP_MEM_ALLOC_UNPROTECT();
    sys_mutex_unlock(&mem_mutex);
    return NULL;
}

#endif /* MEM_USE_POOLS */

#if MEM_LIBC_MALLOC && (!LWIP_STATS || !MEM_STATS)
void *
mem_calloc(mem_size_t count, mem_size_t size)
{
    return mem_clib_calloc(count, size);
}

#else /* MEM_LIBC_MALLOC && (!LWIP_STATS || !MEM_STATS) */
/**
 * Contiguously allocates enough space for count objects that are size bytes
 * of memory each and returns a pointer to the allocated memory.
 *
 * The allocated memory is filled with bytes of value zero.
 *
 * @param count number of objects to allocate
 * @param size size of the objects to allocate
 * @return pointer to allocated memory / NULL pointer if there is an error
 */
void *
mem_calloc(mem_size_t count, mem_size_t size)
{
    void *p;

    /* allocate 'count' objects of size 'size' */
    p = mem_malloc(count * size);
    if (p)
    {
        /* zero the memory */
        memset(p, 0, (size_t)count * (size_t)size);
    }
    return p;
}
#endif /* MEM_LIBC_MALLOC && (!LWIP_STATS || !MEM_STATS) */
